Thin-film capacitor

ABSTRACT

A thin-film capacitor including a stacked body having a lower electrode layer, a plurality of dielectric layers stacked on the lower electrode layer, one or more internal electrode layers interposed between the dielectric layers, and an upper electrode layer that is stacked on the opposite side of the lower electrode layer with the dielectric layers and the internal electrode layers interposed between, and a cover layer that covers the stacked body. The stacked body includes opening portions that have the lower electrode layer, opens upward in a stacking direction, and has a side surface formed to include an inclined surface. The cover layer is stacked on the inclined surface of the stacked body. A curved surface with a predetermined shape is formed on the inclined surface for each pair of layers including the dielectric layer forming the inclined surface and the electrode layer, forming the inclined surface.

TECHNICAL FIELD

The present invention relates to a thin-film capacitor.

BACKGROUND

A multilayer thin-film capacitor in which a dielectric layer and anelectrode layer are alternately stacked on a lower electrode layer andan upper electrode layer is formed thereon is known. In such a thin-filmcapacitor, an insulating cover layer that covers side surfaces of thedielectric layers and the electrode layers is generally formed toprotect the dielectric layers and the electrode layers (for example, seeJapanese Unexamined Patent Publication No. 2000-514243).

SUMMARY

However, in the thin-film capacitor, there is a likelihood that breakageor the like will occur due to separation of the cover layer from astacked body in which the dielectric layers and the electrode layers arestacked.

The invention is made in consideration of the above-mentionedcircumstances and an object thereof is to provide a thin-film capacitorthat can prevent separation of a cover layer from a stacked body.

In order to achieve the above-mentioned object, according to an aspectof the invention, there is provided a thin-film capacitor including astacked body including a lower electrode layer, one or more dielectriclayers that are stacked on the lower electrode layer in a stackingdirection, and one or more internal electrode layers that are stacked onany one of the one or more dielectric layers in the stacking direction,wherein the stacked body includes an opening portion that has the lowerelectrode layer or one electrode layer selected from the one or moreinternal electrode layers as a bottom surface, opens upward in thestacking direction of the electrode layer of the bottom surface, and hasa side surface which is formed to include an inclined surface formed bythe dielectric layer and the electrode layer above the electrode layerof the bottom surface, the inclined surface of the opening portion inthe stacked body is covered with a cover layer, and a curved surfacewith a predetermined shape is formed on the inclined surface for eachpair layer, each pair layer including the dielectric layer forming theinclined surface and the electrode layer, which is stacked on thedielectric layer, forming the inclined surface.

According to the thin-film capacitor, a curved surface with apredetermined shape is formed on the inclined surface of the openingportion of the stacked body for each pair layer including a dielectriclayer and an electrode layer stacked thereon. Accordingly, adhesivenessof the cover layer to the stacked body of the electrode layers and thedielectric layers is improved on the inclined surface of the openingportion. Accordingly, in the thin-film capacitor, it is possible toprevent separation of the cover layer from the stacked body.

Here, the predetermined shape may be a concave shape or a convex shape.

When the shape of the inclined surface is set to a concave shape or aconvex shape as described above, it is possible to more easily form theshape.

The curved surface with the predetermined shape may be formed over theoverall inclined surface which is formed by the pair layers.

Since the curved surface with the predetermined shape is formed over theoverall inclined surface formed by the pair layers as described above,it is possible to further improve adhesiveness to the cover layer and toeffectively prevent separation of the cover layer from the stacked body.

According to the invention, it is possible to provide a thin-filmcapacitor that can prevent separation of a cover layer from a stackedbody.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a thin-film capacitoraccording to an embodiment of the invention;

FIGS. 2A and 2B are diagrams illustrating an inclined surface of thethin-film capacitor;

FIGS. 3A to 3C are diagrams illustrating a method of manufacturing thethin-film capacitor; and

FIGS. 4A and 4B are diagrams illustrating an inclined surface of athin-film capacitor according to a modified example.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the invention will be described in detailwith reference to the accompanying drawings. In description withreference to the drawings, the same elements will be referenced by thesame reference signs and description thereof will not be repeated.

FIG. 1 is a schematic cross-sectional view of a thin-film capacitoraccording to an embodiment of the invention. As illustrated in FIG. 1, athin-film capacitor 100 according to this embodiment includes a lowerelectrode layer 1, three dielectric layers 2, 4, and 6 that are stackedon the lower electrode layer 1, an internal electrode layer 3 that isstacked between the dielectric layer 2 and the dielectric layer 4, aninternal electrode layer 5 that is stacked between the dielectric layer4 and the dielectric layer 6, and an upper electrode layer 7 that isstacked on the opposite side of the lower electrode layer 1 with thedielectric layers 2, 4, and 6 and the internal electrode layers 3 and 5interposed therebetween. The lower electrode layer 1 and the dielectriclayer 2, the internal electrode layer 3, the dielectric layer 4, theinternal electrode layer 5, the dielectric layer 6, and the upperelectrode layer 7 which are sequentially stacked on the lower electrodelayer 1 are together referred to as a stacked body 10. In the followingdescription, a direction in which the dielectric layers and the internalelectrode layers are sequentially superimposed from the lower electrodelayer 1 to the upper electrode layer 7 like the lower electrode layer 1,the dielectric layer 2, and the internal electrode layer 3 is defined asa “stacking direction.” An upper side (upward) in the stacking directionrefers to the upper electrode layer 7 side, and a lower side (downward)in the stacking direction refers to the lower electrode layer 1 side.

The thin-film capacitor 100 includes a pair of terminal electrodes 11and 12 on the opposite side of the lower electrode layer 1 with thedielectric layers 2, 4, and 6, the internal electrode layers 3 and 5,and the upper electrode layer 7 interposed therebetween. The terminalelectrode 11 is electrically connected to the lower electrode layer 1via a via-plug 13 and is electrically connected to the internalelectrode layer 5 via a via-plug 14. The terminal electrode 12 iselectrically connected to the internal electrode layer 3 via a via-plug15 and is electrically connected to the upper electrode layer 7 via avia-plug 16. The pair of terminal electrodes 11 and 12 are electricallyisolated from each other.

The thin-film capacitor 100 includes a cover layer 18 that covers a sidesurface and a top surface of the stacked body including the lowerelectrode layer 1, the dielectric layers 2, 4, and 6, the internalelectrode layers 3 and 5, and the upper electrode layer 7. The coverlayer 18 has only to cover at least the side surface of the stackedbody, and may expose the top surface of the stacked body. The thin-filmcapacitor 100 includes a protective layer 20 that covers a space betweenthe terminal electrodes 11 and 12 and the cover layer 18. Hereinafter,elements constituting the thin-film capacitor 100 will be described.

The lower electrode layer 1 is formed of a conductive material.Specifically, an alloy including nickel (Ni) or platinum (Pt) as a maincomponent can be preferably used as the conductive material of the lowerelectrode layer 1, and particularly an alloy including Ni as a maincomponent can be suitably used. The purity of Ni in the lower electrodelayer 1 is preferably as high as possible and is more preferably equalto or greater than 99.99 wt %. Traces of impurities may be included inthe lower electrode layer 1. Examples of the impurities which can beincluded in the lower electrode layer 1 formed of an alloy including Nias a main component include a transition metal element or rare earthelement such as iron (Fe), titanium (Ti), copper (Cu), aluminum (Al),magnesium (Mg), manganese (Mn), silicon (Si), chromium (Cr), vanadium(V), zinc (Zn), niobium (Nb), tantalum (Ta), yttrium (Y), lanthanum(La), or cesium (Ce), or chlorine (Cl), sulfur (S), or phosphorus (P).

The thickness of the lower electrode layer 1 preferably ranges from 10nm to 100 μmm more preferably ranges from 1 μm to 70 μm, and still morepreferably ranges from 10 μm to 30 μm. When the thickness of the lowerelectrode layer 1 is excessively small, there is a tendency for thelower electrode layer 1 to be difficult to handle at the time ofmanufacturing the thin-film capacitor 100. When the thickness of thelower electrode layer 1 is excessively large, there is a tendency for aneffect of suppressing a leak current to be reduced. The area of thelower electrode layer 1 is, for example, about 1×0.5 mm². The lowerelectrode layer 1 is preferably formed of a metal foil and is usedtogether as a substrate and an electrode. In this way, it is preferablethat the lower electrode layer 1 in this embodiment be configured to bealso used as a substrate, but a substrate/electrode film structure inwhich the lower electrode layer 1 is formed on a substrate formed of Si,alumina, or the like may be employed.

The dielectric layers 2, 4, and 6 are formed of a (ferroelectric)dielectric material having a perovskite structure such as BaTiO₃ (bariumtitanate), (Ba_(1-x)Sr_(x))TiO₃ (barium strontium titanate),(Ba_(1-x)Ca_(x))TiO₃, PbTiO₃, or Pb(Zr_(x)Ti_(1-x))O₃, a complexperovskite relaxer type ferroelectric material such asPb(Mg₁/₃Nb_(2/3))O₃, a bismuth-layered compound such as Bi₄Ti₃O₁₂ orSrBi₂Ta₂O₉, a tungsten-bronze type ferroelectric material such as(Sr_(1-x)Ba_(x))Nb₂O₆ or PbNb₂O₆, or the like. Here, in the perovskitestructure, the complex perovskite relaxer type ferroelectric material,the bismuth-layered compound, and the tungsten-bronze type ferroelectricmaterial, a ratio of A site and B site is normally an integer ratio, butmay be intentionally deviated from the integer ratio for the purpose ofimprovement in characteristics. In order to control characteristics ofthe dielectric layers 2, 4, and 6, additives may be appropriately addedas a secondary component to the dielectric layers 2, 4, and 6.

The thicknesses of the dielectric layers 2, 4, and 6 range, for example,from 10 nm to 1000 nm. The areas of the dielectric layers 2, 4, and 6are, for example, about 0.9×0.5 mm².

The internal electrode layers 3 and 5 interposed between the dielectriclayers 2, 4, and 6 are formed of a conductive material. Specifically, amaterial including nickel (Ni) or platinum (Pt) as a main component canbe preferably used as the conductive material of the internal electrodelayer 3 and 5, and particularly a material including Ni as a maincomponent can be suitably used. When a material including Ni as a maincomponent is used for the internal electrode layers 3 and 5, the contentthereof is preferably equal to or greater than 50 mol % with respect tothe whole internal electrode layers 3 and 5. When a main component ofthe internal electrode layers 3 and 5 is Ni, at least a kind(hereinafter referred to as an “additive element”) selected from a groupconsisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh),ruthenium (Ru), osmium (Os), rhenium (Re), tungsten (W), chromium (Cr),tantalum (Ta), and silver (Ag) is additionally added. Since the internalelectrode layers 3 and 5 include an additive element, breakage of theinternal electrode layers 3 and 5 is prevented. The internal electrodelayers 3 and 5 may include a plurality of kinds of additive elements.

The thicknesses of the internal electrode layers 3 and 5 range, forexample, from 10 nm to 1000 nm. The areas of the internal electrodelayers 3 and 5 are, for example, about 0.9×0.4 mm².

The upper electrode layer 7 is preferably formed of an alloy includingNi as a main component. Traces of impurities may be included in theupper electrode layer 7. Examples of the impurities which can beincluded in the upper electrode layer 7 include a transition metalelement or rare earth element such as iron (Fe), titanium (Ti), copper(Cu), aluminum (Al), magnesium (Mg), manganese (Mn), silicon (Si),chromium (Cr), vanadium (V), zinc (Zn), niobium (Nb), tantalum (Ta),yttrium (Y), lanthanum (La), or cesium (Ce), or chlorine (Cl), sulfur(S), or phosphorus (P). In addition to an alloy including Ni as a maincomponent, platinum (Pt), lead (Pd), iridium (Ir), rhodium (Rh),ruthenium (Ru), osmium (Os), rhenium (Re), titanium (Ti), manganese(Mn), and silver (Ag) other than aluminum (Al), copper (Cu), tungsten(W), chromium (Cr), tantalum (Ta), and niobium (Nb) which are used forwires of a Si semiconductor, a display panel, or the like may be used asthe upper electrode layer 7.

The dielectric layers 2, 4, and 6 are disconnected in the cross sectionof the thin-film capacitor 100 illustrated in FIG. 1, but are continuousin a cross section perpendicular to the stacking direction. Similarly,the internal electrode layers 3 and 5 and the upper electrode layer 7are continuous in a cross section perpendicular to the stackingdirection.

The terminal electrodes 11 and 12 are formed of a conductive materialsuch as copper (Cu). The via-plugs 13, 14, 15, and 16 connected to theterminal electrodes 11 and 12 are formed of a conductive material suchas copper (Cu).

The cover layer 18 can be formed of the same material as the dielectriclayers 2, 4, and 6. That is, a (ferroelectric) dielectric materialhaving a perovskite structure such as BaTiO₃ (barium titanate),(Ba_(1-x)Sr_(x))TiO₃ (barium strontium titanate), (Ba_(1-x)Ca_(x))TiO₃,PbTiO₃, or Pb(Zr_(x)Ti_(1-x))O₃, a complex perovskite relaxer typeferroelectric material such as Pb(Mg₁/₃Nb_(2/3))O₃, a bismuth-layeredcompound such as Bi₄Ti₃O₁₂ or SrBi₂Ta₂O₉, a tungsten-bronze typeferroelectric material such as (Sr_(1-x)Ba_(x))Nb₂O₆ or PbNb₂O₆, or thelike can be suitably used for the cover layer 18. By forming the coverlayer 18 out of the same material as the dielectric layers 2, 4, and 6,it is possible to prevent stress from being generated between the coverlayer 18 and other layers (particularly, the dielectric layers 2, 4, and6 and the like) in contact with the cover layer 18. Accordingly, it ispossible to prevent separation of the cover layer 18 from the otherlayers and thus it is possible to achieve an effect of an increase inelectrostatic capacitance or suppression of a leak current. The materialof the cover layer 18 is not limited to the above-described materials,and an inorganic material such as SiO₂, alumina, or SiN (siliconnitride), an organic material such as polyimide, or an insulatingmaterial in which they are mixed or stacked may be used.

The insulating protective layer 20 disposed between the terminalelectrodes 11 and 12 and the cover layer 18 is formed of, for example,polyimide. By covering the cover layer 18 with the protective layer 20,it is possible to suppress a leak current between the cover layer 18 andthe terminal electrodes 11 and 12. It is preferable that the protectivelayer 20 be disposed between the terminal electrodes 11 and 12 and thecover layer 18 in view of a leak current, but the protective layer 20may not be disposed.

In the thin-film capacitor 100, an opening portion 10A is formed in thestacked body 10 around the via-plug 13 connecting the terminal electrode11 to the lower electrode layer 1. The bottom surface of the openingportion 10A exposes the lower electrode layer 1 which is electricallyconnected to the via-plug 13. The opening portion 10A has the lowerelectrode layer 1 as the bottom surface and opens upward in the stackingdirection (toward the upper electrode layer 7). On the side surface ofthe opening portion 10A, the dielectric layer 2, the internal electrodelayer 3, the dielectric layer 4, the internal electrode layer 5, thedielectric layer 6, and the upper electrode layer 7 in the stackingdirection above the lower electrode layer 1 which is electricallyconnected to the via-plug 13 in the stacked body 10 constitute aninclined surface.

An opening portion 10B is formed in the stacked body 10 around thevia-plug 14 connecting the terminal electrode 11 to the internalelectrode layer 5. The bottom surface of the opening portion 10B exposesthe internal electrode layer 5 which is electrically connected to thevia-plug 14. The opening portion 10B has the internal electrode layer 5as the bottom surface and opens upward in the stacking direction (towardthe upper electrode layer 7). On the side surface of the opening portion10B, the dielectric layer 6 and the upper electrode layer 7 in thestacking direction above the internal electrode layer 5 which iselectrically connected to the via-plug 14 in the stacked body 10constitute an inclined surface.

Similarly, an opening portion 10C is formed in the stacked body 10around the via-plug 15 connecting the terminal electrode 12 to theinternal electrode layer 3. The bottom surface of the opening portion10C exposes the internal electrode layer 3 which is electricallyconnected to the via-plug 15. The opening portion 10C has the internalelectrode layer 3 as the bottom surface and opens upward in the stackingdirection (toward the upper electrode layer 7). On the side surface ofthe opening portion 10C, the dielectric layer 4, the internal electrodelayer 5, the dielectric layer 6, and the upper electrode layer 7 in thestacking direction above the internal electrode layer 3 which iselectrically connected to the via-plug 15 in the stacked body 10constitute an inclined surface.

As described above, the bottom surfaces of the opening portions 10A to10C are formed by the lower electrode layer 1 or one electrode layerselected from the internal electrode layers 3 and 5. The inclinedsurfaces are formed by the dielectric layers and the electrode layers(the internal electrode layers and the upper electrode layer) above thebottom surface.

The opening portion 10A will be described in more detail with referenceto FIGS. 2A and 2B. FIG. 2A is a diagram schematically illustrating thestacked body 10 in the opening portion 10A. FIG. 2B is an enlarged viewof the dielectric layer 2 and the internal electrode layer 3 of thestacked body 10 in the opening portion 10A.

As illustrated in FIG. 2A, on the side surface of the opening portion10A, the inclined surface is formed by the dielectric layer 2, theinternal electrode layer 3, the dielectric layer 4, the internalelectrode layer 5, the dielectric layer 6, and the upper electrode layer7. The inclined surface is formed such that a curved surface with apredetermined pattern is repeated. More specifically, a curved surfacewith a predetermined pattern is formed for each pair layer including onedielectric layer and one electrode layer (one internal electrode layeror the upper electrode layer) stacked thereon. In the opening portion10A, a pair layer 31 is formed by the dielectric layer 2 and theinternal electrode layer 3 stacked thereon. A pair layer 32 is formed bythe dielectric layer 4 and the internal electrode layer 5 stackedthereon. A pair layer 33 is formed by the dielectric layer 6 and theupper electrode layer 7 stacked thereon.

In each of the pair layers 31, 32, and 33, the inclined surface of theopening portion 10A exhibits a concave curved surface as illustrated inFIGS. 2A and 2B. The concave curved surface refers to a curved surfacewhich is concave when the inclined surface is viewed in the stackingdirection. FIGS. 2A and 2B illustrate only the inclined surface of oneside of the opening portion 10A, but a concave curved surface isexhibited for each pair layer on the inclined surfaces forming theopening portion 10B and the opening portion 10C as illustrated in FIG.1.

In the thin-film capacitor 100 according to this embodiment, since theconcave curved surfaces are formed on the inclined surfaces of theopening portions 10A, 10B, and 10C for each pair layer, adhesiveness tothe cover layer 18 covering the inclined surfaces is improved by ananchor effect of the inclined surfaces. As a result, it is possible toachieve an effect of preventing separation of the stacked body 10 havingthe inclined surfaces from the cover layer 18.

The inclined surface of the opening portion 10A will be described belowin more detail. As illustrated in FIG. 2A, it is assumed thatthicknesses (lengths in the stacking direction) of the dielectric layers2, 4, and 6, the internal electrode layers 3 and 5, and the upperelectrode layer 7 are all defined as W1, widths (the lengths in adirection parallel to a plane perpendicular to the stacking direction)of the dielectric layers 2, 4, and 6 are all defined as W2, and widthsof the internal electrode layers 3 and 5 and the upper electrode layer 7are all defined as W3. In this case, when the inclined surface has aconcave shape, a relationship of W2>W3 is satisfied as illustrated inFIG. 2A. As illustrated in FIG. 2A, the length L1 of the concaveinclined surface is larger than the length of a reference line L0, wherea line connecting ends in the stacking direction of the pair layers 31,32, and 33 is defined as the reference line L0. The reference line L0also corresponds to a line connecting ends of the inclined surface.

In a case in which the concave inclined surface is formed for each ofthe pair layers 31, 32, and 33, when an angle of the inclined surface ofthe lower dielectric layer 2 of the pair layer 31 (an angle formed by astraight line connecting an upper end and a lower end and the horizontalplane) is defined as an inclination angle A1 and an angle of theinclined surface of the upper internal electrode layer 3 is defined asan inclination angle A2 as illustrated in FIG. 2B, a relationship ofA1<A2 is satisfied. When an angle formed by the reference line L0 of theinclined surface and the horizontal plane is defined as an inclinationangle A0, a relationship of A1<A0<A2 is satisfied. It is preferable thatthe inclination angle A0 range from 10° to 45°. When the inclinationangle A0 is less than 10°, the inclined surface has a slower inclinationand thus the opening portion increases in size. Since the increase insize of the opening portion causes a decrease in capacity, the size ofthe thin-film capacitor 100 is increased to secure a desired capacity.On the other hand, when the inclination angle A0 is greater than 45°,the inclined surface has an acute angle and thus the size of the openingportion can decrease. On the other hand, since the ends of theneighboring electrode layers with one dielectric layer interposedtherebetween get close to each other, a likelihood that the electrodelayers will short-circuit at the time of processing or the likeincreases. Accordingly, by setting the inclination angle A0 to theabove-mentioned range, it is possible to prevent the electrode layersfrom short-circuiting while preventing an increase in size of theopening portion.

As illustrated in FIG. 2B, a maximum distance (a depth of the inclinedsurface) W4 of the surface of the concave inclined surface from thereference line L0 preferably ranges from 10 nm to 500 nm. By setting themaximum distance W4 of the surface of the inclined surface from thereference line L0 to be equal to or greater than 10 nm, an anchor effectdue to the curved inclined surface can be suitably achieved. On theother hand, when the maximum distance W4 is set to be greater than 500nm, the dielectric layer is greatly cut out as illustrated in FIG. 2B.Since there is a likelihood that the cutting-out of the dielectric layerwill cause a decrease in capacity of the thin-film capacitor 100, thesize of the thin-film capacitor 100 needs to be increased to secure thecapacity. Since the distance between the neighboring electrode layerswith the dielectric layer interposed therebetween decreases, there is alikelihood that short-circuiting will occur. That is, by setting themaximum distance W4 to be equal to or less than 500 nm, it is possibleto secure a desired capacity and to prevent the electrode layers fromshort-circuiting.

When the inclined surface of the opening portion 10A is formed by aplurality of pair layers 31, 32, and 33, the inclination angle of eachpair layer (the reference line) and the inclination angles of theconstituent layers (the dielectric layer and the electrode layer) of thepair layer may be identical for each pair layer or may differ dependingon the pair layers, as illustrated in FIG. 2A. The inclined surfaces ofonly some pair layers of the plurality of pair layers may have have acurved surface. In the thin-film capacitor 100, since the openingportion is formed to surround the corresponding via-plug, it isconsidered that an end face (an area forming the inclined surface) ofeach pair layer actually has an annular shape or a shape obtained byremoving a part from the annular shape. On the other hand, the area inwhich the curved surface is formed for each pair layer may be end facesof the pair layers forming the inclined surface of the opening portion,but the curved surface may be formed in a part of the area. When thecurved surface is formed on the overall end faces of the pair layersforming the inclined surface of the opening portion, it is possible tofurther improve adhesiveness to the cover layer and to further preventseparation of the cover layer from the stacked body.

A method of manufacturing the thin-film capacitor 100 will be describedbelow with reference to FIGS. 3A to 3B. The method of manufacturing thethin-film capacitor 100 includes a step of forming a stacked bodyincluding an opening portion, a step of forming a cover layer, a bakingstep, and a step of forming and connecting a terminal electrode.

First, in the step of forming a stacked body, a metal foil which becomesthe lower electrode layer 1 is prepared. The metal foil is polished suchthat the surface thereof has predetermined arithmetic mean roughness Raif necessary. This polishing can be performed using a method such aschemical mechanical polishing (CMP), electrolytic polishing, or buffpolishing. Then, dielectric films 2 a, 4 a, and 6 a which become thedielectric layers and internal electrode films 3 a and 5 a which becomethe internal electrode layers are alternately formed on the lowerelectrode layer 1.

The composition of the dielectric films 2 a, 4 a, and 6 a is selecteddepending on the dielectric layers 2, 4, and 6 of the completedthin-film capacitor 100. A film forming technique such as a physicalvapor deposition (PVD) method such as a solution method or a sputteringmethod or a chemical vapor deposition (CVD) method can be used as themethod of forming the dielectric films 2 a, 4 a, and 6 a, and thesputtering method is more preferable.

The composition of the internal electrode films 3 a and 5 a is selecteddepending on the internal electrode layers 3 and 5 of the completedthin-film capacitor 100. A DC sputtering method or the like can be usedas the method of forming the internal electrode films 3 a and 5 a.

As illustrated in FIG. 3A, an upper electrode film 7 a is formed on thedielectric film 6 a out of a Ni alloy after the dielectric films 2 a, 4a, and 6 a and the internal electrode films 3 a and 5 a are alternatelystacked. Accordingly, a stacked body 101 in which the lower electrodelayer 1, the dielectric film 2 a, the internal electrode film 3 a, thedielectric film 4 a, the internal electrode film 5 a, the dielectricfilm 6 a, and the upper electrode film 7 a are sequentially stacked isobtained. A DC sputtering method or the like can be used as the methodof forming the upper electrode film 7 a.

Then, opening portions are formed in the stacked body 101. Formation ofthe opening portions is performed by dry etching for each pair layerincluding an upper electrode film (the upper electrode film or theinternal electrode film) and a dielectric film stacked below theelectrode layer. The pair layer corresponds to a pair layer in thethin-film capacitor 100. A resist pattern in which through-holes areformed in predetermined parts is formed on the stacked body 101.Thereafter, etching of an uppermost pair layer is performed using amethod such as reactive ion etching (RIE) or ion milling with the resistpattern as an etching pattern. After etching of one pair layer has beencompleted, the remaining etching pattern is removed.

In order to perform etching such that an end face of the pair layer isconcave like the thin-film capacitor 100, etching rates are controlledsuch that an etching rate of the dielectric film is smaller than anetching rate of the electrode film. The control method is notparticularly limited, but, for example, when Ni is used as the materialof the metal film and BaTiO₃ is used as the material of the dielectricfilm, the above-mentioned relationship can be realized by appropriatelyadjusting a type and a mixing ratio of a reactive gas. In addition, adifference in etching rate between the electrode film and the dielectricfilm can be provided by adjusting a bias voltage, a gas pressure, or asubstrate temperature. For example, by setting etching conditions suchthat the mixing ratio of a halogen reactive gas is small and the biasvoltage is high, a preferable structure (an inclination angle and adepth of a concave inclined surface) in the thin-film capacitor 100according to this embodiment can be realized.

Thereafter, by repeating formation of a resist pattern, etching of onepair layer while performing control of an etching rate, and removal ofthe resist pattern, opening portions 102 to 104 corresponding to theopening portions 10A to 10C can be formed as illustrated in FIG. 3B. Byrepeating etching of one pair layer, an inclined surface in which aconcave curved surface for each pair layer is repeated can be formedlike the opening portions 102 and 104.

Thereafter, a cover film 18 a is formed to cover the surface of thelower electrode film 1 a, the dielectric films 2 a, 4 a, and 6 a, theinternal electrode films 3 a and 5 a, and the upper electrode film 7 a.A material of the cover film 18 a is selected depending on the materialof the cover layer 18. As illustrated in FIG. 3C, the surfaces of theopening portions 102 to 104 and the upper electrode film 7 a in thestacked body 101 are covered by the cover film 18 a.

Thereafter, the stacked body 101 covered with the cover film 18 a isbaked. The baking temperature is preferably set to a temperature atwhich the dielectric films 2 a, 4 a, and 6 a are sintered (crystallized)and preferably ranges from 500° C. to 1000° C. The baking time can beset to 5 minutes to two hours. The baking atmosphere is not particularlylimited, and may be any one of an oxidizing atmosphere, a reducingatmosphere, and a neutral atmosphere. It is preferable that the backingbe performed in at least an oxygen partial pressure in which theelectrode films (the lower electrode film 1 a, the internal electrodefilms 3 a and 5 a, and the upper electrode film 7 a) are not oxidized.Accordingly, the dielectric layers 2, 4, and 6 and the cover layer 18are formed. Formation of an oxide film in an interface between theelectrode film and the dielectric film and an interface between theelectrode film and the cover film is suppressed by baking the dielectricfilms after forming the cover film 18 a.

Then, a protective layer and a terminal electrode are formed andconnected in the backed stacked body. Specifically, the protective layeris stacked on the cover layer 18 of the baked stacked body. Thereafter,the via-plugs 13, 14, 15, and 16 (see FIG. 1) penetrating the protectivelayer and the cover layer are formed. The terminal electrodes 11 and 12(see FIG. 1) are formed to be electrically connected to the via-plugs onthe protective layer. An annealing process may be performed on thestacked body in which the terminal electrodes have been formed. Theannealing process can be performed in the decompressed atmosphere with atemperature of 200° C. to 400° C. The decompressed atmosphere refers toan atmosphere in which the pressure is lower than one atmosphericpressure (=101325 Pa). Electrical characteristics can be stabilized byperforming the annealing process. Accordingly, the thin-film capacitor100 according to this embodiment illustrated in FIG. 1 is obtained.

In this way, in the thin-film capacitor 100 according to thisembodiment, a curved surface with a predetermined pattern is formed foreach of the pair layers 31, 32, and 33 (see FIGS. 2A) including adielectric layer and an electrode layer (the internal electrode layer orthe upper electrode layer) stacked thereon on the inclined surfaces inthe peripheries of the opening portions 10A to 10C of the stacked body10. Accordingly, on the inclined surfaces of the opening portions,adhesiveness of the cover layer 18 to the stacked body 10 of theelectrode layers and the dielectric layers is improved. Accordingly, inthe thin-film capacitor 100, since separation of the cover layer 18 fromthe stacked body 10 is prevented, it is possible to achieve advantageouseffects of improvement in yield or prevention of breakage.

In the thin-film capacitor 100, the patterns of the curved surfaces ofthe pair layers 31, 32, and 33 have a concave shape. When the patternshave a concave shape, the widths (the lengths in a direction parallel toa plane perpendicular to the stacking direction) of the dielectriclayers 2, 4, and 6 are all defined as W2, and the widths of the internalelectrode layers 3 and 5 and the upper electrode layer 7 are all definedas W3 as illustrated in FIG. 2A, a relationship of W2>W3 is satisfied.That is, on the inclined surface, the ratio of the dielectric layers 2,4, and 6 to the internal electrode layers 3 and 5 and the upperelectrode layer 7 increases. In this configuration, for example, whenthe cover layer 18 is formed of the same material as the dielectriclayers 2, 4, and 6, adhesiveness is further improved. Accordingly, it ispossible to further improve adhesiveness of the cover layer 18 to thestacked body 10.

The patterns of the curved surfaces of the pair layers 31, 32, and 33can be formed in a concave shape by controlling the etching rates at thetime of forming the opening portions 102 to 104 in the stacked body 101before being baked. Accordingly, it is possible to manufacture thethin-film capacitor 100 with improved adhesiveness of the cover layer 18to the stacked body 10, for example, without increasing new processingwork such as surface treatment of the inclined surface.

When a curved surface is formed on the overall end faces of the pairlayers forming the inclined surface of the opening portion, it ispossible to further improve adhesiveness of the cover layer 18 to thestacked body 10.

Although it has been described in the above-mentioned embodiment thatthe pattern of the curved surface of each of the pair layers 31, 32, and33 has a concave shape, the pattern of the curved surface is not limitedto the concave shape. As described above in the embodiment, the shape ofthe curved surface of each pair layer can be appropriately changed aslong as a structure capable of improving adhesiveness of the cover layerto the stacked body by an anchor effect of the inclined surface can beobtained.

FIGS. 4A and 4B illustrate a modified example in which the curvedsurface of the inclined surface of the opening portion has a convexshape (a convex shape when viewed in the stacking direction). FIGS. 4Aand 4B are diagrams corresponding to FIGS. 2A and 2B. In the exampleillustrated in FIG. 4A, similarly to FIGS. 2A and 2B, a pair layer 31 isformed by the dielectric layer 2 and the internal electrode layer 3stacked thereon. A pair layer 32 is formed by the dielectric layer 4 andthe internal electrode layer 5 stacked thereon. A pair layer 33 isformed by the dielectric layer 6 and the upper electrode layer 7 stackedthereon. In the modified example illustrated in FIG. 4, the curvedsurface formed by each of the pair layers 31, 32, and 33 has a convexshape.

As illustrated in FIG. 4A, it is assumed that thicknesses (lengths inthe stacking direction) of the dielectric layers 2, 4, and 6, theinternal electrode layers 3 and 5, and the upper electrode layer 7 areall defined as W1, widths (the lengths in a direction parallel to aplane perpendicular to the stacking direction) of the dielectric layers2, 4, and 6 are all defined as W2, and widths of the internal electrodelayers 3 and 5 and the upper electrode layer 7 are all defined as W3.When the inclined surface has a convex shape, a relationship of W2<W3 issatisfied as illustrated in FIG. 4A. As illustrated in FIG. 4A, thelength L2 of the convex inclined surface is larger than the length of areference line L0, where a line connecting ends in the stackingdirection of the pair layers 31, 32, and 33 is defined as the referenceline L0. The reference line L0 also corresponds to a line connectingends of the inclined surface.

In a case in which the convex inclined surface is formed for each of thepair layers 31, 32, and 33, when an angle of the inclined surface of thelower dielectric layer 2 of the pair layer 31 (an angle formed by astraight line connecting an upper end and a lower end and the horizontalplane) is defined as an inclination angle A3 and an angle of theinclined surface of the upper internal electrode layer 3 is defined asan inclination angle A4 as illustrated in FIG. 4B, a relationship ofA3>A4 is satisfied. When an angle formed by the reference line L0 of theinclined surface and the horizontal plane is defined as an inclinationangle A0, a relationship of A3>A0>A4 is satisfied. It is preferable thatthe inclination angle A0 range from 10° to 45°. When the inclinationangle A0 is less than 10°, the inclined surface has a slower inclinationand thus the opening portion increases in size. Since the increase insize of the opening portion causes a decrease in capacity, the size ofthe thin-film capacitor 100 is increased to secure a desired capacity.On the other hand, when the inclination angle A0 is greater than 45°,the inclined surface has an acute angle and thus the size of the openingportion can decrease. On the other hand, since the ends of theneighboring electrode layers with one dielectric layer interposedtherebetween get close to each other, a likelihood that the electrodelayers will short-circuit at the time of processing or the likeincreases. Accordingly, by setting the inclination angle A0 to theabove-mentioned range, it is possible to prevent the electrode layersfrom short-circuiting while preventing an increase in size of theopening portion.

As illustrated in FIG. 4B, a maximum distance (a depth of the inclinedsurface) W5 of the surface of the convex inclined surface from thereference line L0 preferably ranges from 10 nm to 500 nm. By setting themaximum distance W5 of the surface of the inclined surface from thereference line L0 to be equal to or greater than 10 nm, an anchor effectdue to the curved inclined surface can be suitably achieved. On theother hand, when the maximum distance W5 is set to be greater than 500nm, the dielectric layer needs to be left more than the electrode layerand thus the size of the thin-film capacitor 100 needs to be increased.That is, in order to prevent an increase in size of the thin-filmcapacitor 100, it is preferable that the maximum distance W5 be set tobe equal to or less than 500 nm.

One method of forming the inclined surface of an opening portion in thethin-film capacitor 100 as a convex curved surface for each pair layeris controlling the etching rate, similarly to the case of the concaveshape. In order to perform etching such that the inclined surface of theopening portion in the thin-film capacitor has a convex shape for eachpair layer, the etching rate of the dielectric layer is controlled to begreater than the etching rate of the electrode layer. The control methodis not particularly limited, and, for example, when Ni is used as thematerial of the metal layer and BaTiO₃ is used as the material of thedielectric layer, the above-mentioned relationship can be realized byappropriately adjusting a type and a mixing ratio of a reactive gas. Inaddition, a difference in etching rate between the electrode film andthe dielectric film can be provided by adjusting a bias voltage, a gaspressure, or a substrate temperature. For example, by setting etchingconditions such that the mixing ratio of a halogen reactive gas is largeand the bias voltage is low, a preferable structure (an inclinationangle and a depth of a convex inclined surface) in the thin-filmcapacitor 100 according to this embodiment can be realized.

When the inclined surface of each opening portion is formed as a convexcurved surface for each pair layer, it is preferable that the etchingrate be controlled at the final time of repeating formation of a resistpattern, etching of one pair layer, and removal of the resist patternseveral times (the number of times corresponding to the number ofstacked pair layers). By controlling the etching rate at least at thefinal time and performing the etching in a state in which the etchingrate for the electrode layer is greater than the etching rate for thedielectric layer, etching of the dielectric layer of each pair layer ispromoted even when a plurality of pair layers are stacked, and aninclined surface in which the convex curved surface illustrated in FIGS.4A and 4B is repeatedly formed in the stacking direction is formed.

Even when the convex curved surface is formed for each pair layer as inthe modified example illustrated in FIGS. 4A and 4B, adhesiveness of thecover layer to the stacked body is improved by an anchor effect of theinclined surface similarly to the concave curved surface. When theinclined surface is a convex curved surface, a ratio of the internalelectrode layers 3 and 5 to the dielectric layers 2, 4, and 6 and theupper electrode layer 7 on the inclined surface increases. Accordingly,when an inorganic material is used as the material of the cover layer18, it is considered that adhesiveness is particularly increased. Whenthe inclined surface is a concave curved surface, a ratio of thedielectric layers 2, 4, and 6 to the internal electrode layers 3 and 5and the upper electrode layer 7 on the inclined surface is increased.Accordingly, when a dielectric material is used as the material of thecover layer 18, it is considered that adhesiveness is particularlyincreased.

While an embodiment of the invention has been described above, thethin-film capacitor according to the invention is not limited to theembodiment and can be modified in various forms.

For example, in the above-mentioned embodiment, a configuration in whicha plurality of dielectric layers 2, 4, and 6 are stacked on the lowerelectrode layer 1 and the internal electrode layers 3 and 5 are disposedbetween the dielectric layers 2, 4, and 6 has been described, but thethin-film capacitor may have a configuration in which two dielectriclayers are stacked on the lower electrode layer 1 (that is, the numberof internal electrode layers is one). The number of dielectric layersmay be three or more. The number of internal electrode layers is changeddepending on the number of dielectric layers. The number of openingportions is also changed depending on the number of lower electrodelayers and internal electrode layers.

The thin-film capacitor may have a configuration in which no internalelectrode layer is disposed, that is, a configuration in which onedielectric layer is stacked on the lower electrode layer and the upperelectrode layer is stacked thereon. In this case, the upper electrodelayer corresponds to an “internal electrode layer” stacked on at least adielectric layer. Even when the number of dielectric layers is one, thelower electrode layer serves as the bottom surface of the openingportion and a dielectric layer and an electrode layer (the upperelectrode layer) thereon as a pair layer exhibit a curved surface with apredetermined curved surface, whereby adhesiveness to the cover layer 18covering the inclined surface is improved. In this way, the thin-filmcapacitor according to the invention has only to include one or moredielectric layers which are stacked on the lower electrode layer and oneor more internal electrode layers (which may be the upper electrodelayer) which are stacked on the dielectric layers.

Arrangement of the terminal electrodes 11 and 12 and arrangement of thevia-plugs can be appropriately changed. Arrangement of the openingportions can be appropriately changed depending on the arrangement ofthe via-plugs. The inclination angle of the inclined surface can beappropriately changed depending on the arrangement of the openingportions.

The method of manufacturing the thin-film capacitor is not limited tothe above-mentioned embodiment. In the embodiment, a configuration inwhich a plurality of dielectric layers 2, 4, and 6 stacked on the lowerelectrode layer 1 and the cover layer 18 are baked together has beendescribed, but a configuration in which baking is performed severaltimes (for each dielectric layer) or a configuration in which theopening portions are formed after baking may be employed.

The processing method for forming the inclined surface in a curvedsurface for each pair layer is not limited to control of the etchingrate in dry etching as described above. For example, the predeterminedshape of each pair layer may differ depending on the pair layers.Specifically, a pair layer having a convex curved surface and a pairlayer having a concave curved surface may be mixed. Such an embodimentcan be realized by appropriately selecting etching conditions for eachpair layer.

What is claimed is:
 1. A thin-film capacitor comprising: a stacked bodyincluding a lower electrode layer, one or more dielectric layers thatare stacked on the lower electrode layer in a stacking direction, andone or more internal electrode layers that are stacked on any one of theone or more dielectric layers in the stacking direction, wherein thestacked body includes an opening portion that has the lower electrodelayer or one electrode layer selected from the one or more internalelectrode layers as a bottom surface, opens upward in the stackingdirection of the electrode layer of the bottom surface, and has a sidesurface which is formed to include an inclined surface formed by thedielectric layer and the electrode layer above the electrode layer ofthe bottom surface, the inclined surface of the opening portion in thestacked body is covered with a cover layer, and a curved surface with apredetermined shape is formed on the inclined surface for each pairlayer, each pair layer including the dielectric layer forming theinclined surface and the electrode layer, which is stacked on thedielectric layer, forming the inclined surface.
 2. The thin-filmcapacitor according to claim 1, wherein the predetermined shape is aconcave shape or a convex shape.
 3. The thin-film capacitor according toclaim 1, wherein the curved surface with the predetermined shape isformed over the overall inclined surface which is formed by the pairlayers.
 4. The thin-film capacitor according to claim 2, wherein thecurved surface with the predetermined shape is formed over the overallinclined surface which is formed by the pair layers.